Trogocytosis (also referred to as shaving in the literature) is a process by which transfer of membrane-bound proteins and membrane components occur between two different types of live cells associated to form an immunological synapse. As a result, the membrane-bound proteins and membrane components are transferred from the donor cells to the recipient cells. Both unidirectional and bidirectional trogocytosis between the two interacting cells may occur. One prominent example of trogocytosis is the extraction of surface antigens from antigen-presenting cells (APCs) by T cells (Joly & Hudrisier, 2003, Nat Immunol 4:85). The process involves transfer of plasma membrane fragments from the APC to the lymphocyte (Joly & Hudrisier, 2003). Intercellular transfer of T cell surface molecules to APCs has also been reported (Nolte-'t Hoen et al, 2004, Eur J Immunol 34: 3115-25; Busch et al 2008, J Immunol 181: 3965-73) via mechanisms that may include trogocytosis, exosomes and ectodomain shedding (Busch et al 2008, ibid). Trogocytosis can also occur between natural killer (NK) cells and tumors and can convert activated NK cells into suppressor cells, via uptake of the immunosuppressive HLA-G molecule, which protects the tumor cells from cytolysis (Caumartin et al., 2007, EMBO J 26:423-30). CD4+ and CD8+ T cells can, respectively, acquire MHC Class II and MHC Class I molecules from APCs in an antigen-specific manner (Caumartin et al., 2007). Trogocytosis of HLA-DR, CD80 and HLA-G1 from APCs to T cells has been shown to occur in humans (Caumartin et al., 2007). After acquiring HLA-DR and CD80, T cells stimulated resting T cells in an antigen-specific manner, acting as APCs themselves (Caumartin et al., 2007). More generally, trogocytosis may act to regulate immune system responsiveness to disease-associated antigens and can either stimulate or suppress immune response (Ahmed et al., 2008, Cell Mol Immunol 5:261-69).
The effects of trogocytosis on therapeutic antibody responsiveness and the induction of trogocytosis by therapeutic antibodies remain poorly understood. It has been suggested that induction of trogocytosis by excess amounts of rituximab may result in removal of rituximab-CD20 complexes from tumor cell surfaces by monocytes, producing antigenic modulation (shaving) and rituximab-resistant tumor cells (Beum et al., 2006, J Immunol 176:2600-8). Thus, use of lower, more frequent doses of rituximab to reduce antigen shaving has been suggested (Beum et al., 2006). Transfer of rituximab/CD20 complexes to monocytes is mediated by FcγR and it has also been suggested that polymorphisms in FcγRII and FcγRIII may affect the degree of antibody-induced shaving and predict responsiveness to antibody therapy (Beum et al., 2006). In this regard, use of antibodies or other inhibitors that block trogocytosis may enhance efficacy and reduce tumor cell escape from cytotoxicity (Beum et al., 2006). On the other hand, the functional consequences of antibody-mediated trogocytosis to confer therapeutic benefits are less explored.
A need exists in the art for a better understanding of the induction of trogocytosis by therapeutic antibodies, the effect of trogocytosis on antigen shaving, and the effects of trogocytosis and shaving on therapeutic efficacy, target cell susceptibility, and immune system responses in various disease states.